The invention is directed to a vacuum valve in which a valve plate is pressed against a valve seat in the closed state of the valve, so that a valve opening in a wall is closed. This wall can be formed, for example, by a housing wall of the vacuum valve or by the wall of a vacuum chamber, wherein this wall of the vacuum chamber comprising the valve opening and valve seat is therefore considered a part of the vacuum valve. In order to seal the valve opening by means of the valve plate pressing against the valve seat, an elastic sealing ring is provided. This sealing ring can be arranged at the valve plate or at the valve seat. The sealing ring which can be formed, for example, as a circular ring when the valve plate is circular is pressed against a sealing surface in the closed state of the valve. When the sealing ring is arranged at the valve plate, the sealing surface is located at the valve seat. Conversely, the sealing surface is located at the valve plate when the sealing ring is arranged at the valve seat.
Further, the invention is directed to a valve plate for sealing a valve opening in a wall. Further, the invention is directed to a sealing arrangement for a vacuum valve for sealing a valve opening in a wall by means of a valve plate.
Vacuum valves of the plate valve type in which the valve opening is closed by a valve plate which is pressed against the valve seat surrounding the valve opening are known in many different embodiment forms.
A first common embodiment form of plate valves of the type mentioned above is the slide valve. In order to close the valve in this case, the valve plate is initially displaced linearly by an actuation device in a direction transverse to the sealing surface until it is in a position which is located opposite the valve opening, but is lifted from the valve seat. Subsequently, a movement is carried out vertical to the sealing surface and in the direction of the longitudinal axis of the valve opening, so that the valve plate is pressed against the valve seat. This two-step movement process is required so that the seal which is made of an elastic material, e.g., Viton(copyright), is not exposed to shearing stress, which would lead to unacceptable wear. The second step of the closing movement is achieved in different ways in slide valves of the type mentioned above, for example, by means of lever mechanisms, rolling bodies which are guided in wedge-shaped gaps between the valve plate and a supporting plate, tilting elements, and so on. In order to prevent bending of the valve rod during the second movement step (movement vertical to the sealing surface or valve opening), a counterplate is usually provided which is moved simultaneously against a wall located opposite the valve seat. Slide valves of this type are known, for example, from U.S. Pat. No. 4,560,141 A, DE 32 09 217 C2, DE 32 24 387 C2 and U.S. Pat. No. 3,185,435 A.
In a special type of plate valve or slide valve, the second movement step, that is, the movement of the valve plate against the valve seat by a movement directed essentially vertical to the sealing surface, is carried out in that the valve rod is swiveled about a fulcrum. This fulcrum can be formed by pins or rollers which are arranged laterally at the valve rod and guided in guide grooves. Accordingly, the valve rod is constructed in this instance in the manner of a lever which is initially displaced linearly and is then tilted. Examples of valve constructions of this type are shown in U.S. Pat. No. 5,415,376 A, U.S. Pat. No. 5,641,149 A, U.S. Pat. No. 6,045,117 A, U.S. Pat. No. 5,934,646 A, U.S. Pat. No. 5,755,255 A, U.S. Pat. No. 6,082,706 A and U.S. Pat. No. 6,095,180 A.
In another type of plate valve, there is no linear displacement of the valve plate in the first step of the valve plate movement; rather, the valve plate is swiveled along an arc in order to move the valve plate into the position located opposite the valve opening. For this purpose, the valve rod is suspended by its end opposite the valve plate at a shaft so as to be swivelable about an axis extending vertical to the valve face. The second step of the closing movement of the valve plate in the direction of the valve seat is carried out by a linear displacement of this shaft.
Another known type of plate valve is the angle valve, as it is called. In this valve, the valve rod to which the valve plate is secured is guided out of the vacuum through a wall located opposite the valve opening by means of a suitable lead-through.
Sealing rings made of elastic material are known for scaling the valve. A commonly used material for the sealing rings is known by the trade name Viton(copyright), but scaling rings made from other materials arc also common. The sealing rings are adapted to the respective circumferential contour of the valve plate and can thus be constructed, for example, in circular shape or can have other circumferentially closed contours, for example, approximately corresponding to the circumferential contour of a rectangle with rounded corners.
In conventional vacuum valves, the full contact pressure force with which the valve plate is pressed against the valve seat normally acts on the sealing ring in the closed state of the valve. In particular, when a differential pressure between the two areas which are sealed relative to one another acts upon the valve plate, there are considerable forces acting upon the sealing ring. These forces can far exceed the required sealing force. The sealing force is that force which must be exerted on the sealing ring in order to achieve sealing. In the event that differential forces of varying magnitude can act upon the valve plate, the force exerted on the sealing ring in these conventional constructions must at least equal the sealing force plus the force occurring as a result of maximum differential pressure. This contact pressing force is also exerted on the sealing ring when there is no differential pressure at all opposing the contact pressing force, so that a very high stress is exerted on the sealing ring in this case. This results in relatively rapid wear of the elastic material of the sealing ring. This problem is exacerbated when corrosive process gases are used. It has been determined that the elastic materials commonly used for the seals are chemically corroded by aggressive process gases particularly when they are under high stress.
Therefore, it has already been suggested to provide path limiting in the drive for the valve plate which limits the deformation of the elastic material of the sealing ringxe2x80x94independent from occurring differential pressurexe2x80x94to a predetermined value. However, path limiting of this type for very small paths to be monitored can only be realized at great expenditure and is, moreover, susceptible to disturbances.
Further, EP 1 028 278 A2 discloses a valve seal arrangement which shields the sealing ring from process gases. In this case, a protective seal which is constructed, for example, in the shape of a plate is provided in addition to the sealing ring and essentially completely covers the valve opening in the closed state of the valve. The edge of this flat protective seal is pressed against the surface surrounding the opening by the tension of the deformed sealing ring. Also, the deformation of the sealing ring in the closed state of the valve can be limited by this construction.
It is further known to provide the valve disk with a metal projection which is formed integral with the valve disk and which contacts a surface surrounding the valve opening in the closed state of the valve. This limits the deformation of the sealing ring. However, the contact of the metal projection of the valve plate at the surface, likewise made of metal, which surrounds the valve opening leads to unwanted release of particles adhering to the metal surfaces into the vacuum or onto parts located in the vacuum which are sensitive to impurities (such as wafers with high-purity surfaces).
A primary object of the present invention is to provide a vacuum valve of the type mentioned above in which the deformation of the sealing ring is limited in the closed state of the valve. The vacuum valve should also be constructed in a simple manner and there should be no unnecessary release of particles into the vacuum when the valve is closed. The invention has the further object of shielding the sealing ring from corrosive process gases in a vacuum valve of the type mentioned above in a simple manner. A further object of the invention is to provide a valve plate for sealing a valve opening in a wall in which the deformation of the sealing ring is limited in the closed state of the valve opening, wherein the valve plate has a simple construction and an unnecessary release of particles is prevented in the closed state of the valve. Another object of the invention is to provide a simple construction of a valve plate of the type mentioned above in which the sealing ring is shielded from process gases in the closed state of the valve opening.
The invention has the further object of providing a sealing arrangement for a vacuum valve for sealing a valve opening in a wall by means of a valve plate by which, in a simple construction of the sealing arrangement, the deformation of the sealing ring is limited in the closed state of the valve opening and the sealing ring is shielded from process gases.
A vacuum valve according to the invention comprises a supporting ring which is made of plastic and arranged at the valve plate or at the valve seat and, at least in the closed state of the vacuum valve, lies closer to the opening than the sealing ring viewed from the sealing ring, and which, in the closed state of the vacuum valve, limits the contact pressing force acting on the sealing ring. Further, a supporting ring of this kind shields the sealing ring from process gases in the closed state of the valve. When the valve is closed, there is no metal-on-metal contact between the valve plate and the valve seat, so that a release of particles is reduced when closing the valve. In a valve plate according to the invention, a supporting ring made of plastic is provided at the valve plate such that this supporting ring, viewed from the sealing ring, is arranged closer to the lateral surface of the valve plate than the sealing ring when the valve is open and limits pressing force acting on the sealing ring in the closed state of the valve plate.
In a preferred embodiment example of the invention, the supporting ring is connected to the sealing ring and is formed integral therewith. In other embodiment forms of the invention, the sealing ring and the supporting ring are constructed as separate parts.
The various features and constructions according to the invention are indicated in the claims.